[tptacek]

One way to look at this is that companies go upmarket from a firm base of downmarket customers. There's a lot of uncertainty in upmarket enterprise sales: the engagements can involve RFPs or bakeoffs and involve dogfights that incumbents can lose to upstarts. A company can do really well in the high-end markets without ever having a stable, defensible customer base in it.

So if Trello grows to the point where it seriously threatens Jira's downmarket base, Atlassian has two problems: first, that Trello is sapping their downmarket revenue, but second, that Trello then has a beachhead from which to start attacking their high-end prospects as well.

"Killing Atlassian" is surely easier said than done, and probably hyperbolic. But buying Trello to prevent the emergence of a credible competitor to them across all their important markets? That sounds like a pretty plausible explanation for the valuation.

I'm a little skeptical, though, if only because I think Trello has a lot more potential than Jira (and of Jira's value proposition in the abstract). I think Atlassian just bought the next Microsoft Excel.